Simultaneous cellulose conversion and hydrogen production assisted by cellulose decomposition under UV-light photocatalysis

Photocatalytic conversion of cellulose to sugars and carbon dioxide with simultaneous production of hydrogen assisted by cellulose decomposition under UV or solar light irradiation was achieved upon immobilization of cellulose onto a TiO2 photocatalyst. This approach enables production of hydrogen from water without using valuable sacrificial agents, and provides the possibility for recovering sugars as liquid fuels.

Controlled periodic illumination in semiconductor photocatalysis

Controlled periodic illumination is a hypothesis postulated in the early 1990s for enhancing the efficiency of semiconductor photocatalytic reactions. This technique has been proposed to improve photocatalytic efficiency by the nature of photon introduction alone. Before its application in semiconductor photocatalysis, controlled periodic illumination had been investigated in other fields including photosynthesis. This paper presents a detailed review of the state of the art research undertaken on the application of controlled periodic illumination in semiconductor photocatalysis. The review briefly introduces semiconductor photocatalysis, and then presents a detailed explanation of this technique, its importance to photocatalytic efficiency, an overview of previous results of its application in significant studies and present knowledge. Results from previous as well as some of the most recent studies indicate potential applications of controlled periodic illumination in areas other than just the improvement of the efficiency of the photocatalytic process.

Gas-phase photocatalytic oxidation of dichlorobutenes

Gas-phase photocatalysis of 1,4-dichlorobut-2-enes and 3,4-dichlorobut-1-ene (DCB) has been studied using TiO2 and 3%WO3/TiO2 supported on SiO2. DCB was found to oxidize efficiently over these catalysts; however, only low rates of CO2 formation were observed. With these chlorinated hydrocarbons, the catalysts were found to deactivate over time, probably via the formation of aldol condensation products of chloroacetaldehyde, which is the predominant intermediate observed. The variation in rate and selectivity of the oxidation reactions with O-2 concentration is reported and a mechanism is proposed. Using isotope ratio mass spectrometry, the initial step for the DCB removal has been shown not to be a carbon bond cleavage but is likely to be hydroxyl radical addition to the carbon-carbon double bond.

UV-activated photocatalyst films and inks for cleaning tarnished metals

A simple UV-activated, TiO2-based film or ink for removing thin oxide or sulfide layers from metal surfaces by reductive photocatalysis is described.

Simple method for the rapid simultaneous screening of photocatalytic activity over multiple positions of self-cleaning films

An intelligent ink, previously shown to be capable of rapidly assessing photocatalytic activity, was simply applied via a felt-pen onto a commercially available piece of Activ (TM) self-cleaning glass. The ink, comprising of redox dye resazurin and the sacrificial electron donor glycerol within an aqueous hydroxy ethyl cellulose (HEC) polymer media, was photocatalytically degraded in a two-step process. The key initial stage was the photo-reductive conversion of resazurin to resorufin, whereby a colour change from blue to pink occurred. The latter stage was the subsequent photo-reduction of the resorufin, where a slower change from pink to colourless was seen. Red and green components of red-green-blue colour extracted from flat-bed scanner digital images of resazurin ink coated photocatalytic films at intervals during the photocatalysis reaction were inversely proportional to the changes seen via UV-visible absorption spectroscopy and indicative of reaction kinetics. A 3 x 3 grid of intelligent ink was drawn onto a piece of Activ (TM) and a glass blank. The photocatalysis reaction was monitored solely by flat-bed digital scanning. Red-green-blue values of respective positions on the grid were extracted using a custom-built program entitled RGB Extractor (c). The program was capable of extracting a number of 5 x 5 pixel averages of red-green-blue components simultaneously. Allocation of merely three coordinates allowed for the automatic generation of a grid, with scroll-bars controlling the number of positions to be extracted on the grid formed. No significant change in red and green components for any position on the glass blank was observed; however, the Activ (TM) film displayed a homogenous photo-reduction of the dye, reaching maxima in red and minima in green components in 23 +/- 3 and 14 +/- 2 min, respectively. A compositionally graded N-doped titania film synthesised in house via a combinatorial APCVD reaction was also photocatalytically tested by this method where 247 positions on a 13 x 19 grid were simultaneously analysed. The dramatic variation in photocatalysis observed was rapidly quantified for all positions (2-3 hours) allowing for correlations to be made between thicknesses and N : Ti% compositions attained from Swanepoel and WDX analysis, respectively. N incorporation within this system was found to be detrimental to film activity for the photocatalysis reaction of intelligent ink under 365 nm light.

A study of new photocatalyst indicator inks

This article reports the behaviour of three photocatalyst indicator inks, based on the redox dyes: methylene blue (NIB), resorufin (Rf) and 2,6-dichloroindophenol (DCIP), and assess their performance in comparison to the pioneering resazurin (Rz)-based ink for the rapid assessment of the activity of very thin, photocatalyst films, such as Activ (TM) self-cleaning glass. From a commercial 'demonstrator of photocatalysis' perspective, all three redox dyes appear more attractive compared to Rz since all generate colourless products in the ink formulation when photoreduced on Activ (TM) under anaerobic conditions, whereas, the reduced product from Rz, the redox dye resorufin, Rf. is pink in colour. However, the ink based on Rf is far too slow to effect the rapid measurement of photocatalytic activity even in the absence of oxygen, and in the presence of oxygen the latter inhibits the overall kinetics of photoreduction by re-oxidising the reduced product, dihydroresorufin, HRf, back to Rf. Similarly, despite the attractive rapid rate of photobleaching for NIB under anaerobic conditions, compared to the other redox dyes, the reduced product of the MB-based ink. leuco-MB, is so oxygen-sensitive that the ink cannot be photoreduced under aerobic conditions, thus rendering the ink unsuitable for use in the field. The DCIP-based ink is slightly less easy to photoreduce under both anaerobic and ambient atmospheric conditions compared to the Rz-based ink. However. in addition to its more attractive colour change, the DCIP-based ink is unaffected by the ambient level of oxygen present (%O-2) and the relative humidity (%RH), whereas, for the Rz-based ink, both parameters effect the photoreduction kinetics. By incorporating the DCIP ink into a felt-tipped pen, the ink is suitable for use in the laboratory and field to perform not only a qualitative test, but also to allow a semi-quantitative analysis of photocatalytic activity by eye. (C) 2007 Elsevier B.V. All rights reserved.